Evaluation of PCR and nested PCR assays currently used for detection of Coxiella burnetii in Japan.

Detection of Coxiella burnetii, the etiologic agent of Q fever, is important for diagnosis of Q fever. PCR-based methods have been widely used for the detection mostly because isolation of C. burnetii is time-consuming. Recent reports showed that PCR-positive rates of Q fever infection widely differed. We have evaluated the PCR and nested PCR assays currently used in Japan. The nested PCR assay detected as few as 6 microorganisms and was 10 times more sensitive than the regular PCR assay. The nested PCR assay did not show any non-specific bands with 12 other bacteria, whereas the PCR assay showed some extra bands for 5 of the 12 bacteria. These results suggest that the nested PCR is more sensitive and specific than the PCR in the detection of C. burnetii. However, nested PCR generally has a risk of cross-contamination during preparation of the 2nd PCR. Using blood specimens serially col- lected from an acute Q fever patient, the PCR and the nested PCR assays gave very similar results, suggesting that sensitivity of the PCR assay is at an achieved level of the detection for clinical speci- mens although the nested PCR assay is more sensitive. It is recommended that both the PCR and nested PCR assays should be performed for the detection of C. burnetii to obtain reliable results.